The silicon based ceramics are becoming increasingly important members of the class of materials that are referred to in the United States as advanced ceramics or high performance ceramics and in Japan as "fine ceramics". These materials, which include silicon carbide, silicon nitride, and sialon, are useful both in their monolithic forms as well as when used as the reinforcing phase in ceramic or metal matrix composites. The silicon based ceramics, or composites containing these materials, are the leading candidates for a wide range of applications, including service at both modest and elevated temperatures in such devices as advanced heat engines and heat exchangers. In heat engines these ceramics can be used in wear reducing parts for conventional gasoline or diesel engines, including components such as bearings, valve rocker arm pads, push rod tips, or camshaft roller followers, as well as for in-cylinder components for low heat rejection diesel engines. They could also be useful as small ceramic turbine rotors in the turbocharger of conventional gasoline engines or in relatively small, high efficiency, advanced gas turbine engines that could be used in automobiles or as the auxiliary power units in aircraft. These materials are also of interest in heat exchangers that recover the waste heat from a variety of industrial processes. Finally, there is increasing interest in ceramic cutting tools including those made of silicon nitride, and silicon carbide whisker reinforced alumina, one of the most widely studied composite materials.
Although other factors such as corrosion resistance may occasionally dictate the use of a ceramic for these and other applications, a key factor that is almost always of interest is the strength of the material. Ceramic materials may be strengthened by alloying additions or through steps taken to minimize grain growth, but even then they fail to attain their full potential because of strength limiting surface flaws that are inevitably introduced during fabrication. There is a need, therefore, to improve the strength of silicon based ceramics by a process that can be applied after all conventional fabrication steps have been taken.